Difference between Primary key,unique key,Alternate Key?

 Posted by Sriramnandha on 6/3/2012 | Category: Sql Server Interview questions | Views: 10095 | Points: 40

Primary Key ==> Is used to uniquely identify records and doesn't allow NULL values.

Unique Key ==> Is also used to uniquely identify records but does allow NULL Values per column combination.

Alternate Key ==> Is another type of Unique key, which is used to identify each record uniquely. This is not a constraint. This is just a terminology.

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